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These environments differ markedly from Earth's gravity in several key aspects:
# Absence of natural convection: On Earth, density differences in fluids due to temperature gradients drive [[natural convection]]. In microgravity, this effect is negligible, leading to diffusion-dominated heat and mass transfer.<ref name="auto1">{{Cite book |url=https://doi.org/10.1016/B978-0-08-044508-3.X5000-2 |title=Fluids, Materials and Microgravity |date=2004 |publisher=Elsevier |isbn=978-0-08-044508-3 |doi=10.1016/b978-0-08-044508-3.x5000-2}}</ref>
# Surface tension dominance: Without the overwhelming force of gravity, [[surface tension]] becomes a dominant force in fluid behavior, significantly affecting liquid spreading and containment.<ref>{{Cite book |last=Myshkis |first=A. D. |url=http://archive.org/details/lowgravityfluidm0000mysh |title=Low-Gravity Fluid Mechanics: Mathematical |date=1987-06-02 |publisher=Springer |others=Internet Archive |isbn=978-3-540-16189-9}}</ref>
# Particle suspension: In low-gravity environments, particles in fluids remain suspended for extended periods, as [[sedimentation]] and [[buoyancy]] effects are minimal.<ref name=":0">{{Cite journal |last=Todd |first=P. |date=1989-08-02 |title=Gravity-dependent phenomena at the scale of the single cell |url=https://pubmed.ncbi.nlm.nih.gov/11540086/ |journal=ASGSB bulletin: publication of the American Society for Gravitational and Space Biology |volume=2 |pages=95–113 |issn=0898-4697 |pmid=11540086}}</ref>
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==== Material behavior ====
Low-gravity environments offer unique conditions for materials processing. The absence of buoyancy-driven convection and sedimentation allows for more uniform crystal growth and the formation of novel alloys and composites.<ref>{{Cite book |url=https://link.springer.com/book/9781468416855 |title=Materials Processing in Space |language=en}}</ref> Additionally, the reduced [[Stress (mechanics)|mechanical stresses]] in microgravity can lead to changes in material properties and behavior, influencing fields such as [[materials science]] and [[pharmaceutical research]].<ref name="auto">{{Cite journal |last=Ronney |first=Paul D. |date=1998-01-01 |title=Understanding combustion processes through microgravity research |url=https://www.sciencedirect.com/science/article/pii/S008207849880101X |journal=Symposium (International) on Combustion |volume=27 |issue=2 |pages=2485–2506 |doi=10.1016/S0082-0784(98)80101-X |issn=0082-0784}}</ref>
== Challenges ==
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#Reduced convective heat transfer: Without buoyancy-driven flows, heat transfer becomes primarily dependent on conduction and [[radiation]], potentially leading to localized hot spots and thermal management issues.<ref name=":9">{{Cite journal |last=Berto |first=Arianna |last2=Azzolin |first2=Marco |last3=Bortolin |first3=Stefano |last4=Miscevic |first4=Marc |last5=Lavieille |first5=Pascal |last6=Del Col |first6=Davide |date=2023-04-04 |title=Condensation heat transfer in microgravity conditions |url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10073138/ |journal=NPJ Microgravity |volume=9 |pages=32 |doi=10.1038/s41526-023-00276-1 |issn=2373-8065 |pmid=37015948}}</ref>
# Boiling and condensation: These [[Phase transition|phase change]] processes behave differently in microgravity, affecting cooling systems and thermal management strategies.<ref
# Temperature gradients: The absence of natural mixing can result in sharp [[temperature gradient]]s, impacting reaction kinetics and material processing.<ref
=== Material handling and containment difficulties ===
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# Particle behavior: Without settling due to gravity, particles tend to remain suspended and disperse differently, affecting filtration, separation, and mixing processes.<ref name=":0" />
# Liquid containment: Surface tension effects can cause liquids to adhere unexpectedly to container walls, complicating storage and transfer operations.<ref
# Phase separation: The lack of density-driven separation makes it challenging to separate immiscible fluids or different phases of materials.<ref name=":1" />
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[[Chemical engineering]] processes in microgravity often exhibit different behaviors compared to their terrestrial counterparts.
[[Chemical kinetics|Reaction kinetics]] in microgravity can be altered due to the absence of buoyancy-driven [[convection]]. This can lead to more uniform reaction conditions and potentially different reaction rates or product distributions.<ref
Separation processes, such as distillation and extraction, face unique challenges in low-gravity environments. The lack of buoyancy affects phase separation and mass transfer, requiring novel approaches to achieve efficient separations.<ref>{{Cite journal |last=Chakavarti |first=Bulbul |last2=Chakavarti |first2=Deb |date=2008-06-12 |title=Electrophoretic separation of proteins |url=https://pubmed.ncbi.nlm.nih.gov/19066548/ |journal=Journal of Visualized Experiments: JoVE |issue=16 |pages=758 |doi=10.3791/758 |issn=1940-087X |pmc=2583038 |pmid=19066548}}</ref> These challenges have led to the development of alternative separation technologies for space applications.<ref>{{Cite journal |last=Martin |first=Gary |last2=Rhome |first2=Robert |date=1995-01-09 |title=Microgravity research in a space station environment |url=https://arc.aiaa.org/doi/10.2514/6.1995-388 |journal=33rd Aerospace Sciences Meeting and Exhibit |language=en |publisher=American Institute of Aeronautics and Astronautics |doi=10.2514/6.1995-388}}</ref>
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